Divine Smite

You may make a Heavy Attack that deals Holy Damage against the target. If your target’s HP is lower than the max damage your attack would deal, this attack gains Full Pierce and does maximum damage instead of rolling.

This calculation only involves your base damage (Base weapon damage + the power). Any other effects added to the damage such as Heavy Blade's bonus damage, Anathema on target etc do not affect the calculation and aren't maximized.